Klompmaker, A.A., Starzyk, N., Fraaije, R.H.B., and Schweigert, G. 2020. Systematics and convergent evolution of multiple reef-associated Jurassic and Cretaceous crabs (Decapoda, Brachyura). Palaeontologia Electronica 23(2): a32.
We studied multiple true crabs (Brachyura) from primarily sponge and coral reefs that lived during the Jurassic and Cretaceous periods (201 to 66 million years ago). Both environments were important habitats for the evolution and biodiversity of crabs during the Late Jurassic epoch (164 to 145 million years ago). The central portion of the crabs, called the carapace, is used to study these crabs. We described one new genus and five new species. One species was named after UA Museums Research Associate Dr. Cristina Robins. Other taxa are redescribed in more detail, synonymized (four species), or reassigned (three species and two genera). After studying details of the carapace of closely and distantly related groups of crabs, we found similarities and differences among distantly related groups. The similarities in the rostrum might be a sign of their independent adaptation or convergent evolution in this context. In one case, we found very strong similarities between specimens of genera that were placed in two different superfamilies. We placed these taxa in the same family again and argue against extreme convergent evolution. We also report on a remarkably large parasitic swelling made by an isopod in one crab’s gill region, and we show the largest complete Jurassic crab carapace reported thus far.
Kiel, S., Hybertsen, F., Hyžný, M., and Klompmaker, A.A. 2020. Mollusks and a crustacean from early Oligocene methane-seep deposits in the Talara Basin, northern Peru. Acta Palaeontologica Polonica 65: 109–138.
Methane seeps are places on the ocean floor where methane escapes from the subsurface into the water column. Such seeps, also called cold seeps, can be found at different depths in the oceans today and in the past. They are essentially the cold equivalent of hydrothermal vents. Bacteria and other organisms, such as clams and tube worms living in symbiosis with these bacteria, feed on this methane and create local hotspots of biodiversity. Seeps attract a variety of organisms such as fishes, gastropods, echinoderms, and crustaceans. Research on modern and fossil methane seeps has been booming over the last decade. We report on a ~30 million-year-old seep fauna from Peru. We describe 25 species of bivalves, gastropods, and crustaceans, bringing the total local seep fauna close to 40 species. Among those species, six species (2 bivalves, 3 gastropods, and 1 ghost shrimp) and one genus are new to science. Many genera in this hotspot of biodiversity can also be found in the northeastern Pacific around that time, showing a biogeographic connection to that area.
Wallaard, J.J.W., Fraaije, R.H.B., Jagt, J.W.M., Klompmaker, A.A., and Van Bakel, B.W.M. 2020. The first record of a paguroid shield (Anomura, Annuntidiogenidae) from the Miocene of Cyprus. Geologija 63: 93–99.
Fossil hermit crabs (Paguroidea) have long been known from the fossil record, primarily from claws. Over the last ten years, their millimeter-sized shields (particularly the anterior part) have been increasingly recognized. As a result, researchers have since described over 30 new species from the Late Jurassic and mid-Cretaceous (~160–100 million years ago), particularly from coral reefs. Hermit crab shields were unknown from the Miocene (23–5 million years ago) until this paper. Fraaije and Klompmaker did field work in 2017 in ~10 million old fossil reefs exposed on Cyprus (eastern Mediterranean Sea) and found one shield of a paguroid. This shield represents a new hermit crab species, named Paguristes joecollinsi. This is just the first species from a rich crustacean reef fauna, so stay tuned for more papers in years to come!
Ehret, D. and Harrell, Jr., T.L. 2018. Feeding traces on Pteranodon (Reptilia: Pterosauria) bone from the late Cretaceous (Campanian) Mooreville Chalk in Alabama, USA. PALAIOS 33: 414–418.
The Pteranodon specimen exhibits serrated teeth marks on the surface of the bone and a second set of larger, unserrated teeth marks unlike those of any contemporary shark species. These feeding traces compare favorably with the tooth spacing and morphology of Squalicorax kaupi, and a small to moderate-sized saurodontid fish, such as Saurodon or Saurocephalus, respectively. In both instances, feeding traces appear to be scavenging events due to the lack of any healing or bone remodeling. During the Campanian, Dallas County, Alabama, was a shallow-marine environment comprising part of the Mississippi Embayment. It is hypothesized that the specimen represents a pterosaur that either fell into marine waters or was washed out from nearshore areas and then scavenged by both a chondrichthyan and osteichthyan. This type of scavenging behavior has been recorded on other taxonomic groups from Alabama during the Late Cretaceous. However, the fragile, hollow bones of pterosaurs make their preservation rare.
(2018) Development of polymorphic microsatellite markers for a rare dragonfly, Cordulegaster sarracenia (Odonata: Cordulegastridae), with notes on population structure and genetic diversity. International Journal of Odonatology 21: 165–171.
We isolated and characterized a total of 13 microsatellite loci from Cordulegaster sarracenia (Odonata: Cordulegastridae). Loci were screened in 24 individuals from Louisiana and Texas. Within C. sarracenia, the number of alleles per locus ranged from 0 to 5, and observed and expected heterozygosities ranged from 0.000 to 0.556 and 0.000 to 0.613, respectively. Overall differentiation among study populations was very high (FST = 0.423), suggesting significant geographic population structure with low diversity within populations. Twelve of the 13 primers amplified in C. sayi, C. diastatops, C. maculata, and C. obliqua and polymorphism levels are reported. These new genetic markers will provide tools for addressing a number of population genetic and demographic questions relating to conservation of this rare dragonfly species.
Field, D.J., Hanson, M., Burnham, D., Wilson, L.E., Super, K., Ehret, D., Ebersole, J., and Bhullar, B.-A.S., 2018. Complete Ichthyornis skull illuminates mosaic assembly of the avian head. Nature 557: 96–100.
The skull of living birds is greatly modified from the condition found in their dinosaurian antecedents. Bird skulls have an enlarged, toothless premaxillary beak and an intricate kinetic system that includes a mobile palate and jaw suspensorium. The expanded avian neurocranium protects an enlarged brain and is flanked by reduced jaw adductor muscles. However, the order of appearance of these features and the nature of their earliest manifestations remain unknown. The Late Cretaceous toothed bird Ichthyornis dispar sits in a pivotal phylogenetic position outside living groups: it is close to the extant avian radiation but retains numerous ancestral characters. Although its evolutionary importance continues to be affirmed, no substantial new cranial material of I. dispar has been described beyond incomplete remains recovered in the 1870s. Jurassic and Cretaceous Lagerstätten have yielded important avialan fossils, but their skulls are typically crushed and distorted. Here we report four three-dimensionally preserved specimens of I. dispar— including an unusually complete skull—as well as two previously overlooked elements from the Yale Peabody Museum holotype, YPM 1450.
We used these specimens to generate a nearly complete three-dimensional reconstruction of the I. dispar skull using high resolution computed tomography. Our study reveals that I. dispar had a transitional beak—small, lacking a palatal shelf and restricted to the tips of the jaws—coupled with a kinetic system similar to that of living birds. The feeding apparatus of extant birds therefore evolved earlier than previously thought and its components were functionally and developmentally coordinated. The brain was relatively modern, but the temporal region was unexpectedly dinosaurian: it retained a large adductor chamber bounded dorsally by substantial bony remnants of the ancestral reptilian upper temporal fenestra. This combination of features documents that important attributes of the avian brain and palate evolved before the reduction of jaw musculature and the full transformation of the beak.